Electrochemical detection of mixture solutions of As3+ and As5+ has been investigated by stripping voltammetry at gold-modified diamond electrodes. The method was performed based on stripping oxidation of As-0 deposited at the electrode surface. Whereas As3+ can be deposited by simple electrochemical reduction of As3+ to As-0 at -0.4 V (vs. Ag/AgCl), much higher potential is required to overcome the activation energy of As5+ reduction. However, in such a high potential, hydrogen evolution also occurs. Consequently, one more step should be added to release the hydrogen gas adsorbed at the electrode surface during the reduction step. During the deposition of As5+, AS(3+) species was also simultaneously deposited. Therefore, to differentiate AS(3+) and As5+ quantification in a mixture solution, both stripping voltammetry methods should be performed and calculated mathematically. Comparison of stripping voltammograms of both methods for As3+ solution in the absence of As5+ demonstrated similar peak shapes and current intensities, confirming that error calculation of As5+ concentration in the mixture solution with As3+ can be avoided. Good linear responses were observed for each standard solution of As3+ and As5+. Linear calibration curve could also be achieved for a series concentrations of 100-1000 ppb AS(5+) in a mixture solution with 100 ppb As3+ (r(2) = 0.99) and for a series concentrations of 5-30 ppb As3+ in a mixture solution with 100 ppb As5+. Detection limits of 5 and 100 ppb can be achieved for As3+ and As5+ in a mixture solution, respectively. The reproducibility was shown for stripping voltammetry of As3+ and As5+ with an RSD (n = 8) of 7.5% and 8.4%,, respectively. Good stability of gold-modified diamond electrodes before and after arsenic detection was also evaluated by SEM image. Application of the method for real sample analysis was performed for arsenic detection in Yokohama tap water. (C) 2008 Elsevier B.V. All rights reserved.